The purpose of the proposed research is to study the physical- chemical properties of the enamel-saliva system which have a bearing on the cariogenic process. In particular, studies will be conducted on: 1. The characterization of enamel and its water as a diffusion medium. Water vapor adsorption isotherms for intact enamel sections will be used for the purpose from which information will be obtained on porosity, pore geometry, pore volume distribution, and the thermodynamic properties of the water. The effect of the organic matter on the enamel properties, related to transport processes, will be investigated. 2. The actual diffusional processes through dental enamel. Microdiffusion cells (diaphragm-type) will be used for this purpose with enamel sections as the septum. Electrostatic and steric interactions will be distinguished by using charged and uncharged diffusing particles of different sizes. Comparative studies will be conducted in the presence and absence of adsorbed salivary pellicles. 3. The permselective nature of salivary constituents. EMF measurements in concentration cells will be employed. The salivary constituents will be adsorbed on an apatitic membrane separating the cell compartments. 4. Adsorption isotherms of purified salivary proteins on synthetic apatites. Information will be derived on their affinities and adsorption capacities which will be used to gain insight into the nature of the integument on the very surface the tooth enamel. The possible effect of fluoride content of the adsorbent will be investigated. 5. The effect of adsorbed salivary pellicles on the rates of solution and precipitation of enamel and synthetic apatites. The results will be related to demineralization and remineralization processes in the oral environment. 6. The incorporation of the above approaches into a proposed model to explain the formation of incipient carious lesions. Subsurface lesions will be developed on teeth, in vitro, in the presence and absence of salivary pellicles, and under a variety of conditions as dictated by the findings of the above studies.